The NAD-dependent histone deacetylase Sirt1 antagonizes p53 transcriptional activity to regulate cell-cycle progression and apoptosis. We have identified a ubiquitin-specific peptidase, USP22, one of the 11 death-from-cancer signature genes that are critical in controlling cell growth and death, as a positive regulator of Sirt1. USP22 interacts with and stabilizes Sirt1 by removing polyubiquitin chains conjugated onto Sirt1. The USP22-mediated stabilization of Sirt1 leads to decreasing levels of p53 acetylation and suppression of p53-mediated functions. In contrast, depletion of endogenous USP22 by RNA interference destabilizes Sirt1, inhibits Sirt1-mediated deacetylation of p53 and elevates p53-dependent apoptosis. Genetic deletion of the usp22 gene results in Sirt1 instability, elevated p53 transcriptional activity and early embryonic lethality in mice. Our study elucidates a molecular mechanism in suppression of cell apoptosis by stabilizing Sirt1 in response to DNA damage and reveals a critical physiological function of USP22 in mouse embryonic development.

In rheumatoid arthritis (RA), macrophage is one of the major sources of inflammatory mediators. Macrophages produce inflammatory cytokines through toll‐like receptor (TLR)‐mediated signalling during RA. Herein, we studied macrophages from the synovial fluid of RA patients and observed a significant increase in activation of inositol‐requiring enzyme 1α (IRE1α), a primary unfolded protein response (UPR) transducer. Myeloid‐specific deletion of the IRE1α gene protected mice from inflammatory arthritis, and treatment with the IRE1α‐specific inhibitor 4U8C attenuated joint inflammation in mice. IRE1α was required for optimal production of pro‐inflammatory cytokines as evidenced by impaired TLR‐induced cytokine production in IRE1α‐null macrophages and neutrophils. Further analyses demonstrated that tumour necrosis factor (TNF) receptor‐associated factor 6 (TRAF6) plays a key role in TLR‐mediated IRE1α activation by catalysing IRE1α ubiquitination and blocking the recruitment of protein phosphatase 2A (PP2A), a phosphatase that inhibits IRE1α phosphorylation. In summary, we discovered a novel regulatory axis through TRAF6‐mediated IRE1α ubiquitination in regulating TLR‐induced IRE1α activation in pro‐inflammatory cytokine production, and demonstrated that IRE1α is a potential therapeutic target for inflammatory arthritis.

Background: Stroke is accompanied by a distinguished inflammatory reaction that is initiated by the infiltration of immunocytes, expression of cytokines, and other inflammatory mediators. As natural killer cells (NK cells) are a type of cytotoxic lymphocyte critical to the innate immune system, we investigated the mechanism of NK cells-induced brain injuries after cerebral ischemia and the chemotactic effect of IP-10 simultaneously. Methods: NK cells infiltration, interferon-gamma (IFN-γ) and IP-10 expression were detected by immunohistochemistry, immunofluorescence, PCR and flow cytometry in human and C57/BL6 wild type mouse ischemic brain tissues. The ischemia area was detected via 2,3,5-triphenyltetrazolium chloride staining. CXCR3 mean fluorescence intensity of isolated NK cells was measured by flow cytometry. The neuronal injury made by NK cells was examined via apoptosis experiment. The chemotactic of IP-10 was detected by migration and permeability assays. Results: In human ischemic brain tissue, infiltrations of NK cells were observed and reached a peak at 2 to 5 days. In a permanent middle cerebral artery occlusion (pMCAO) model, infiltration of NK cells into the ischemic infarct region reached their highest levels 12 hours after ischemia. IFN-γ-positive NK cells and levels of the chemokine IP-10 were also detected within the ischemic region, from 6 hours up to 4 days after pMCAO was performed, and IFN-γ levels decreased after NK cells depletion in vivo. Co-culture experiments of neural cells with NK cells also showed that neural necrosis was induced via IFN-γ. In parallel experiments with IP-10, the presence of CXCR3 indicates that NK cells were affected by IP-10 via CXCR3, and the effect was dose-dependent. After IP-10 depletion in vivo, NK cells decreased. In migration assays and permeability experiments, disintegration of the blood-brain barrier (BBB) was observed following the addition of NK cells. Moreover, in the presence of IP-10 this injury was aggravated. Conclusions: All findings support the hypothesis that NK cells participate in cerebral ischemia and promote neural cells necrosis via IFN-γ. Moreover, IP-10 intensifies injury to the BBB by NK cells via CXCR3.

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The type III histone deacetylase sirtuin 1 (Sirt1) is a suppressor of both innate and adoptive immune responses. We have recently found that Sirt1 expression is highly induced in anergic T cells. However, the transcriptional program to regulate Sirt1 expression in T cells remains uncharacterized. Here we report that the early responsive genes 2 and 3, which can be up-regulated by T-cell receptor-mediated activation of nuclear factor of activated T-cell transcription factors and are involved in peripheral T-cell tolerance, bind to the sirt1 promoter to transcript sirt1 mRNA. In addition, the forkhead transcription factor, FoxO3a, interacts with early responsive genes 2/3 on the sirt1 promoter to synergistically regulate Sirt1 expression. Interestingly, IL-2, a cytokine that can reverse T-cell anergy, suppresses sirt1 transcription by sequestering FoxO3a to the cytoplasm through activating the PI3K-AKT pathway. Expression of the constitutively active form of FoxO3a blocks IL-2-mediated reversal of T-cell tolerance by retaining sirt1 expression. Our findings here provide a molecular explanation of IL-2-mediated reversion of T-cell anergy.